INFUSORIA. 



113 



lateral. They are sufficiently large to be observe! by the common 

 lens, or eye-glass. Paramecium aurelia appears chiefly in vege- 

 table infusions. It is common in ditches and moats with aquatic 

 plants. 



Humboldt's assertion is fully verified in the case of the Infusoria 

 under consideration, which is often found with its parasites. These 

 are small creatures, cylindrical in form, and provided with suckers. 

 Swimming vigorously in the water, they devote themselves to chasing 

 the Paramecium. When they have overtaken the fugitive, they 

 throw themselves upon it, and establish themselves there. They soon 

 multiply in the interior of its body, and their starving progeny suck 

 and devour the unfortunate animalcule, which serves them at once 

 for dwelling-house and larder. 



Another of the parasites which prey upon the Paramecium, in 

 place of pursuing it, remains perfectly quiet until one of these 

 approach, when it throws itself 

 upon its victim, and is carried 

 along with it. It buries itself 

 in the body of the Paramecium, 

 and, in a short time; multiplies 

 to such a degree, that some- 

 times fifty of them are found 

 on a single individual. Poor 

 victim ! 



The Nassula have the body 

 entirely covered with cilia ; they 

 are ovoid or oblong in form, con- 

 tractile, the mouth placed late- 

 rally and dentate, or surrounded 

 with a band of horny bristles, 

 the band dilating and contract- 

 ing according to the size of the 

 prey which it would swallow. 

 It either advances to seize the 

 prey, which the movement of 

 vibratile cilia have failed to draw 



within the vortex of its mouth, or, as in the case of the Paramecium, 

 it is sometimes obliged to seek for its prey. These curious infusoria 





